When printing iregs, there was a double newline printed because
perf_sample__fprintf_regs() was printing its own and then at the end of
all fields, perf script was adding one.  This was causing blank line in
the output:

Before:

  $ perf script -Fip,iregs
             401b8d ABI:2    DX:0x100    SI:0x4a8340    DI:0x4a9340

             401b8d ABI:2    DX:0x100    SI:0x4a9340    DI:0x4a8340

             401b8d ABI:2    DX:0x100    SI:0x4a8340    DI:0x4a9340

             401b8d ABI:2    DX:0x100    SI:0x4a9340    DI:0x4a8340

After:

  $ perf script -Fip,iregs
             401b8d ABI:2    DX:0x100    SI:0x4a8340    DI:0x4a9340
             401b8d ABI:2    DX:0x100    SI:0x4a9340    DI:0x4a8340
             401b8d ABI:2    DX:0x100    SI:0x4a8340    DI:0x4a9340

Committer testing:

First we need to figure out how to request that registers be recorded,
so we use:

  # perf record -h reg

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

      -I, --intr-regs[=<any register>]
                            sample selected machine registers on interrupt, use '-I?' to list register names
          --buildid-all     Record build-id of all DSOs regardless of hits
          --user-regs[=<any register>]
                            sample selected machine registers on interrupt, use '--user-regs=?' to list register names

  #

Ok, now lets ask for them all:

  # perf record -a --intr-regs --user-regs sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 4.105 MB perf.data (2760 samples) ]
  #

Lets look at the first 6 output lines:

  # perf script -Fip,iregs | head -6
   ffffffff8a06f2f4 ABI:2    AX:0xffffd168fee0a980    BX:0xffff8a23b087f000    CX:0xfffeb69aaeb25d73    DX:0xffff8a253e8310f0    SI:0xfffffff9bafe7359    DI:0xffffb1690204fb10    BP:0xffffd168fee0a950    SP:0xffffb1690204fb88    IP:0xffffffff8a06f2f4 FLAGS:0x4e    CS:0x10    SS:0x18    R8:0x1495f0a91129a    R9:0xffff8a23b087f000   R10:0x1   R11:0xffffffff   R12:0x0   R13:0xffff8a253e827e00   R14:0xffffd168fee0aa5c   R15:0xffffd168fee0a980

   ffffffff8a06f2f4 ABI:2    AX:0x0    BX:0xffffd168fee0a950    CX:0x5684cc1118491900    DX:0x0    SI:0xffffd168fee0a9d0    DI:0x202    BP:0xffffb1690204fd70    SP:0xffffb1690204fd20    IP:0xffffffff8a06f2f4 FLAGS:0x24e    CS:0x10    SS:0x18    R8:0x0    R9:0xffffd168fee0a9d0   R10:0x1   R11:0xffffffff   R12:0xffffffff8a23e480   R13:0xffff8a23b087f240   R14:0xffff8a23b087f000   R15:0xffffd168fee0a950

   ffffffff8a06f2f4 ABI:2    AX:0x0    BX:0x0    CX:0x7f25f334335b    DX:0x0    SI:0x2400    DI:0x4    BP:0x7fff5f264570    SP:0x7fff5f264538    IP:0xffffffff8a06f2f4 FLAGS:0x24e    CS:0x10    SS:0x2b    R8:0x0    R9:0x2312d20   R10:0x0   R11:0x246   R12:0x22cc0e0   R13:0x0   R14:0x0   R15:0x22d0780

  #

Reproduced, apply the patch and:

[root@five ~]# perf script -Fip,iregs | head -6
 ffffffff8a06f2f4 ABI:2    AX:0xffffd168fee0a980    BX:0xffff8a23b087f000    CX:0xfffeb69aaeb25d73    DX:0xffff8a253e8310f0    SI:0xfffffff9bafe7359    DI:0xffffb1690204fb10    BP:0xffffd168fee0a950    SP:0xffffb1690204fb88    IP:0xffffffff8a06f2f4 FLAGS:0x4e    CS:0x10    SS:0x18    R8:0x1495f0a91129a    R9:0xffff8a23b087f000   R10:0x1   R11:0xffffffff   R12:0x0   R13:0xffff8a253e827e00   R14:0xffffd168fee0aa5c   R15:0xffffd168fee0a980
 ffffffff8a06f2f4 ABI:2    AX:0x0    BX:0xffffd168fee0a950    CX:0x5684cc1118491900    DX:0x0    SI:0xffffd168fee0a9d0    DI:0x202    BP:0xffffb1690204fd70    SP:0xffffb1690204fd20    IP:0xffffffff8a06f2f4 FLAGS:0x24e    CS:0x10    SS:0x18    R8:0x0    R9:0xffffd168fee0a9d0   R10:0x1   R11:0xffffffff   R12:0xffffffff8a23e480   R13:0xffff8a23b087f240   R14:0xffff8a23b087f000   R15:0xffffd168fee0a950
 ffffffff8a06f2f4 ABI:2    AX:0x0    BX:0x0    CX:0x7f25f334335b    DX:0x0    SI:0x2400    DI:0x4    BP:0x7fff5f264570    SP:0x7fff5f264538    IP:0xffffffff8a06f2f4 FLAGS:0x24e    CS:0x10    SS:0x2b    R8:0x0    R9:0x2312d20   R10:0x0   R11:0x246   R12:0x22cc0e0   R13:0x0   R14:0x0   R15:0x22d0780
 ffffffff8a24074b ABI:2    AX:0xcb    BX:0xcb    CX:0x0    DX:0x0    SI:0xffffb1690204ff58    DI:0xcb    BP:0xffffb1690204ff58    SP:0xffffb1690204ff40    IP:0xffffffff8a24074b FLAGS:0x24e    CS:0x10    SS:0x18    R8:0x0    R9:0x0   R10:0x0   R11:0x0   R12:0x0   R13:0x0   R14:0x0   R15:0x0
 ffffffff8a310600 ABI:2    AX:0x0    BX:0xffffffff8b8c39a0    CX:0x0    DX:0xffff8a2503890300    SI:0xffffb1690204ff20    DI:0xffff8a23e4080000    BP:0xffff8a23e4080000    SP:0xffffb1690204fec0    IP:0xffffffff8a310600 FLAGS:0x28e    CS:0x10    SS:0x18    R8:0x0    R9:0x0   R10:0x0   R11:0x0   R12:0xffffffffffffffea   R13:0xffff8a23e4080020   R14:0x0   R15:0x0
 ffffffff8a11b688 ABI:2    AX:0x0    BX:0xffff8a237b7c8800    CX:0xffffb1690204fae0    DX:0x78    SI:0xffff8a237b7c8800    DI:0xffffb1690204fa10    BP:0xffffb1690204fb00    SP:0xffffb1690204fa00    IP:0xffffffff8a11b688 FLAGS:0x8a    CS:0x10    SS:0x18    R8:0x1495f0a917eba    R9:0xffffd168fde19a48   R10:0xffffb1690204fd98   R11:0xffff8a253e82afb0   R12:0xffff8a237b7c8800   R13:0xffffb1690204fb00   R14:0x0   R15:0xffff8a237b7c8800
[root@five ~]#

To see it more clearly, lets get just two of those registers by sample:

  # perf record -a --intr-regs=ax,bx --user-regs=cx,dx sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 3.502 MB perf.data (1653 samples) ]
  #

Extra info, lets see what gets setup in that 'struct perf_event_attr':

  # perf evlist -v
  cycles: size: 120, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|CPU|PERIOD|REGS_USER|REGS_INTR, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, task: 1, precise_ip: 2, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1, sample_regs_user: 0xc, sample_regs_intr: 0x3
  #

Cook, some PERF_SAMPLE_REGS_USER|PERF_SAMPLE_REGS_INTR +
attr.sample_regs_user and attr.sample_regs_intr register masks, now lets
see if those newlines are gone in a more compact fashion:

  # perf script -Fip,iregs,uregs
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a29b78d ABI:2    AX:0x2a20ffcd6000    BX:0x2ec7d9000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
  #

And where was that?

  # perf script -Fip,iregs,uregs,sym,dso
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a56df78 strrchr (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0xffff8a25137b6028    BX:0xffff8a2502f18000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
   ffffffff8a29b78d __vma_link_rb (/lib/modules/5.7.0-rc2/build/vmlinux) ABI:2    AX:0x2a20ffcd6000    BX:0x2ec7d9000  ABI:2    CX:0x7f204460e49b    DX:0xf42920
  #
Signed-off-by: NStephane Eranian <eranian@google.com>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200418231908.152212-1-eranian@google.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>